Machine translation in which a computer converts text (sentence) inputted by a human into a text (sentence) in a language of another country is widely used, but in cases dealing with conversion within the same language, a text (sentence) paraphrasing method for converting a text (sentence) expression is used (refer to Non-Patent Document 1).
Non-Patent Document 1 describes one example of a conventional text paraphrasing expression creating method. The text paraphrasing expression creating method described in Non-Patent Document 1 is a method in which a human creates in advance a paraphrasing rule expressed by syntactic features (properties). Ultimately confirmation by a human is required for an obtained paraphrase expression.
In addition, with regard to a text paraphrasing method, a question and answer system that automatically outputs an answer with respect to a converted question, or the like, is also used (refer to Patent Document 1). For example, Patent Document 1 describes one example of a text paraphrase expression creating method for obtaining a text (sentence) paraphrase model by machine learning from a paraphrase corpus. In the text paraphrase expression creating method described in Patent Document 1, a plurality of explanatory texts with respect to the same headline in a newspaper article or a dictionary are regarded as different text pairs in which description contents match. That is, a paraphrase corpus is created by regarding the explanatory texts with respect to the same headline as text (sentence) pairs in a paraphrase relationship, and machine learning is performed thereon.    [Non-Patent Document 1]    Fujita, Atsushi, et al., “A Class-oriented Approach to Building a Paraphrase Corpus”, Proceedings of the 3rd International Workshop on Paraphrasing (IWP), October, 2005, pp. 25-32.    [Patent Document 1]    JP Patent Kokai Publication No. JP-P2002-014990A (paragraphs 0058-0059, FIG. 4).